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Messages - Charlie Carpenter

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The bottom line:

A couple of facts:

To provide a perfect Airy disk:

- The focuser does not need to be "squared."

- The secondary does not need to be "perfectly" centered. ''

As far as Nils and Vic Menard disagreeing on the importance of squaring the focuser, I don't think so.

"In fact, the only good reasons I can think of to "square" and offset the secondary mirror in such a way that the optical axis is closely aligned to the OTA axis is for optimal DSC performance or when aligning a compound Newtonian with a corrector at the front aperture."

If one wants to square the focuser, go ahead and do it. If one wants to set the focuser at 91 degrees to the OTA, go ahead and do it.

Jon Isaacs

Beginners Forum / Re: First Time Telescope Buyer
« on: February 09, 2018, 06:30:40 AM »
I started in this hobby 8 months ago so I have recently been through the same research you are doing now.

First, what is your budget? Without that we can only guess. You say the Meade 102 is over your budget at about $229. But then you list the Orion XT8 classic which is $390, so I am confused.

Is there someone among your group who is knowledgeable about astronomy?

Where will you store the telescope? How will you transport it?

Either of the refractors is a valid choice.  Easy to use, simple to set-up and relatively small to store.  If your skies are fairly dark and you want something small and easy to set-up and transport the Meade Infinity 90 would be a good choice as a shared item. The Infinity 90 received Sky and Telescope Innovative Astronomy Gear recognition in Jan 2016 Sky and Telescope.  Naturally the 102 would gather more light.  For a shared instrument I like these better.

The main benefit of the Dobsonian XT8 is the aperture. 8"/203 mm XT8 has about 5X the light gathering ability of the 90 mm refractor. Telescopes are all about gathering light. But it is bigger, bulkier. Because of that it will be harder to store and harder to move about as a shared resource.

If you do feel you can go with an XT8 type scope I would also suggest you consider the Zhumell Z8. My friend has one and it is quite nice and comes with a better focuser and better finder scope than the XT8 classic Dob.
http://www.telescope...ector-telescopeI own the Orion XT8i Intelliscope. I like it very much. Same optics as the XT8 you mentioned but mine has computer assist to help me find the things I want to see. If you had the budget I would recommend this one.  As a community tool among people who don't have a lot of background in astronomy the computer assist could be very helpful.

Using the Intelliscope Computer Object Locatorhttp://s7d5.scene7.c...niversal_Video1
Attached is a photo of my 3 scopes, for size comparison.

Closest is the XT8i. Weighs about 45 pounds. Stands about 55" tall. My daughter calls it my cannon. 

Second is the Meade ETX 80. 400 mm FL 80 mm refractor, about 12 pounds. The Meade 90 or 102 would be a bit bigger than this.

Third is a 76 mm Tasco reflector. 

Just for size comparison.

I messed up big time  ..... ! Kill the copy paste.... the original question was to ask ..... and i... thought that XT8.. Cause this is equivalent to an Meade infinity 90mm..

Accurate PA with an EQ-6 style PAS.

1) Check PAS alignment with the RA shaft by placing the PAS crosshairs on a distant object and making sure that the object stays exactly centred in the crosshairs while you rotate the mount in RA. If not you'll need to adjust the PAS reticule.

Level the tripod base plate

2) Place the mount in the home position (OTA pointed exactly due north, CW shaft at lowest point) . Rotate your RA setting circle until it reads 24 hours.

3)place Polaris exactly centred on the cross hair in your PAS using your alt/az adjusters.

Note the position of the small circle (where Polaris will be placed) Rotate the mount in RA until the small circle is at the 12/24 oclock position (midnight on a 12 or 24 hr scale). Using the azimuth adjuster confirm that Polaris will move east or west while staying exactly on the cross hairs and rotate the RA shaft until Polaris will stay on the line (this can be done during the day using a small distant object). This is your PAS home position. Make a note of the RA setting circle reading in hours and minutes*. This is the RA offset needed to place your PAS in it's home position. Write it down!

4) With the PAS in it's home position, and with Polaris centred on the crosshair. Look up the (24hr not 12!)) hour angle of Polaris (the HC will display it IIRC). Set the RA setting circle to 24. Watching the RA setting circle rotate the mount in RA the required number of hours - this will place the small circle at the correct hour angle.

5) Using the Alt/az adjusters place Polaris into the small circle. Lock your alt/az adjusters.

6) you are now PAed to the limits of accuracy of your PAS (typically under ~5 arc minutes but probably closer to ~2).* you can use the HC RA/Dec readout if your mount doesn't have setting circles.

Beginners Forum / Re: Seeing Sirius B?
« on: February 08, 2018, 09:31:16 PM »
I think anything you tried to occluded the scope with would be out of focus, unless you had a tiny little disk at the focal plane of your eyepiece (probably mounted on an optical flat). That might work although some of the scatter would have already taken place, and you'd need very precise tracking to keep it over Sirius A.

Looks very promising. The big unknown is howit willhold up over a decade or so...the reason I'm put off with Lumicon.

I also notice on their site that they have "introductory pricing" of $109.95 for the 1.25". Looks like a filter that will out do the Lumicon at a lower price. My non-Lumicon 2" UHC is holding up, but I could use a 1.25" which would also replace my dubious Lumicon O-III.

Beginners Forum / Re: Just Realized Humidity Stinks
« on: February 03, 2018, 07:31:21 AM »
<p class="citation">QuoteJust Realized Humidity Stinks[/quote]

Come to Savannah, and you learn that in about 30 minutes, regardless of the time of day.

5 minutes if it's June-September.

3 minutes if it's August.


Reflectors Telescopes Forum / Re: Dobson 10" for planets/moon ?
« on: February 02, 2018, 08:38:25 PM »
Four factors are going to be your constraints. Sky conditions and optics quality have been mentioned. The other 2 are collimation. If sky conditions and optics are great but you're even off on your collimation is off a smidge it's going to affect your visual results.

Well, maybe a movie where all the ghosts, monsters, hobgoblins, and boogymen attacked during the day instead of at night...

Mounts Questions & Expirience / Re: Has the CGEM mount changed much?
« on: January 31, 2018, 01:31:13 PM »
No not all mounts had the coging problem. Only some. I have had 5 different CGEMs and none of the ones I owned had the problem.


ATM, Optics and DIY Forum / Re: So, I hope to make a 6" Gregorian or two
« on: January 31, 2018, 11:58:44 AM »
I'm signed up for the Delmarva mirror making class next month. Now I need to figure out what I'm bringing. I have several 6" blanks and kits in various stages of completion, but I was hoping to make me a Gregorian or two, or maybe a Greg and a Cass out of two of the blanks.

Here's where it all begins:


By all means go for it.You'll love your Greg.I have a 6 inch f/31 and gives me wonderful views.
Delmarva uses AC so getting an excellent mirror is within grasp...


You can use a straight edge clamp to saw against or if you ain't got one just use a straight edge &amp; a couple of clamps.

Beginners Forum / Re: Red or green for preserving night vision?
« on: January 31, 2018, 05:28:00 AM »
To your original search, the Xtra Dark Cling on this page works well on iPhones and iPads: http://www.siriusast...ght-shield.html

Thank you Wyatt, this is what I originally set out to find.

Funny the site mentions rubylith, I used it many years ago when I worked with screen printing and that's what I had in mind when I started my search.

Eyepieces Questions & Recommendations / Re: Meade HD-60 18mm
« on: January 31, 2018, 05:16:16 AM »
You probably should have said that to start with. - It would have saved us both some time.

Apologies, I shared that on another thread with many of the same audience so didn't feel like repeating myself.

My first hand experience with these budget 6 element in 4 group oculars is that they do have some subtle differences but not enough to think any is in a different class than another.

My current line up includes three of the Xcel LXs and I have owned two of the Paradigms. As soon as some bills are paid I plan on picking up the 6.5mm Meade.

You can tell I like this design but will readily agree they won't compete with the Televue and Pentax offerings. But for my budget I am quite pleased.

Beginners Forum / Re: ES102 Carbon Fiber as a grab and go?
« on: January 31, 2018, 04:06:21 AM »
Makes sense, so if the conditions aren't the limiting factor the 8" will do better since it will have a brighter image at higher magnification, but under average to poor conditions the 4" will do better since its looking through smaller section of sky?
Sort of. The larger the scope the more of the bad atmosphere you are looking through. But there is also the magnification factor. The 4"/102mm is a f/7 with a focal length of 714mm. The 8"/203mm is an f/10 and has a focal length of 2,032mm. Power aka magnification is calculated by dividing the focal length of the scope by the focal length of the eyepiece. A 14mm eyepiece on the 102 generates 51x (714/14). The same EP in the SCT generates 145x (2032/14). So you are looking at an object in the SCT with a magnification that is (just under) three times that of the 102mm. So you will "see" more of the distortion aka poor seeing/transparency in the air.There are other factors as well. Optically the reflecting telescope will have a lower overall light transmission due to the central obstruction than the refracting telescope. The reflecting scope may not be collimated and even slight moves outside of "good collimation" will mean a diminished quality of view. And there is also the cool down. Both scopes will have tube currents but the heat radiated off of the glass in the smaller APO will be different (and much faster) in its speed of decrease to ambient than the larger mirrored one. Both because of the size of the scope and because that mirror is a big heat sink.<p class="citation">QuoteI actually did contact ES about the TW1, they first said it would be fine, but they also said to try and keep it under 12lbs total with accessories. The 102 essential would be over that, just the OTA and mounting bracket is 11lbs. The CF would be close to 12lbs, maybe a little over with a heavy 2" EP, but at really low power a little vibration might be ok.[/quote]You big 2" EP's, unless they are 100* ES's will be low power so your vibration should be limited. For what it's worth I would use a 11" EdgeHD visually on a AVX. The AVX was on a driveway. I would use the vibration suppression pads and it would dampen the vibrations very quickly even at high power. So they work very well.

The Zhumell site says that the mirror is 250mm. Don't know how much wiggle room the focuser gives you, I don't know much about that.

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